reserve m for Cardinal,
  A,B,C for Ordinal,
  x,y,z,X,Y,Z,W for set,
  f for Function;

theorem Th19:
  W is Tarski implies card W is limit_ordinal
proof
  assume
A1: W is Tarski;
  now
    let A;
    assume A in card W;
    then A in W by A1,Th13;
    then succ A in W by A1,Th5;
    then succ A in On W by ORDINAL1:def 9;
    hence succ A in card W by A1,Th9;
  end;
  hence thesis by ORDINAL1:28;
end;
